20 Years of Data Show Poultry, Fish, Beef Have Remained Leading Sources of Food-Related Outbreaks

Between 1998 and 2008, poultry, fish and beef were consistently responsible for the greatest proportion of foodborne illness outbreaks, according to a new government analysis.

Experts at the Centers for Disease Control and Prevention reviewed the 13,405 food-related outbreaks reported during this time period, identifying 3,264 outbreaks that could be attributed to a specific food category. Fish and poultry remained responsible for the greatest share of these outbreaks over these 20 years — accounting for about 17 percent of outbreaks each — followed closely by beef, which was responsible for 14 percent of outbreaks.

Eggs, on the other hand, played an increasingly smaller role as outbreak sources – accounting for 6 percent of outbreaks in 1998-1999 and for just 2 percent in 2006-2008. This trend was largely due to a decrease in the amount of Salmonella outbreaks linked to eggs, according to the report authors.

Leafy greens became a more common outbreak source, responsible for 6 percent of outbreaks in 1998-1999 and 11 percent by 2008-2009. Dairy also grew as an outbreak source, rising from 4 percent in the beginning of the period studied to 6 percent by 2006-2008.

The researchers also looked at the leading pathogen-food combinations that caused outbreaks during the 20-year window, finding that histamine in fish was the most common outbreak source, followed by ciguatoxin in fish, Salmonella in poultry and norovirus in leafy vegetables.

“You see the same combinations of pathogens and foods repeatedly,” said Hannah Gould, epidemiologist in the Division of Foodborne, Waterborne, and Environmental Diseases at CDC’s National Center for Emerging and Zoonotic Infectious Diseases and lead author of the report. “It’s good to keep tracking that and now to have a method to continue to look at changes over time,” Gould commented in an interview with Food Safety News.

The authors note that the number of outbreaks linked to these commodities should not be confused with the number of illnesses caused by these foods, as outbreaks result in varying numbers of illnesses.

While poultry was responsible for the largest share of illnesses (17 percent) between 1998 and 2008, leafy greens were the next greatest cause of illness, accounting for 13 percent of the 67,752 illnesses attributed to an outbreak food source.

The pathogen/commodity pairs responsible for the most outbreak-related illnesses were norovirus and leafy vegetables, which led to 4,011 illnesses of the 67,752 linked to a designated commodity category.

The team also looked at food preparation, finding that restaurants and delis accounted for the vast majority (68 percent) of the places where outbreak-linked foods were prepared. Private homes were the next most common place of preparation, at 9 percent, followed by catering or banquet facilities (7 percent).

“That’s something interesting that we talk about here more than we usually do,” said Gould, referring to the location data, which CDC doesn’t often report in its reviews of foodborne illness data.

Outbreaks after 2008

What about outbreaks that have occurred since 2008? Have these trends continued or have they changed in the past few years?

“Leafy greens and norovirus continues to be a problem and norovirus has been the number one cause of outbreaks in our data for years and years and years and has remained that way,” said Gould.

Gould also led an analysis of foodborne illness outbreaks that occurred between 2009 and 2010 — published in January of this year — which found that during that period, beef, dairy, fish, and poultry were associated with the largest number of foodborne disease outbreaks.

That report also showed that unpasteurized dairy products are the leading cause of dairy-related outbreaks, accounting for 81 percent of the outbreaks linked to dairy during that time period. Gould said the 1998-2008 report shows that the incidence of raw dairy-related outbreaks has been growing over this time.

“Outbreaks caused by dairy went up as well, and that seems to be caused by an increasing number of outbreaks due to unpasteurized milk,” she said.

The data used for this report comes from CDC’s Foodborne Disease Outbreak Surveillance System, which was started by CDC in 1973 and went online in 1998. The authors chose 1998-2008 as their reporting period because the format of the database changed starting in 2008, when it became the National Outbreak Reporting System.